1. Field of the Invention
The present invention relates to an ultrasonic-wave delay element. More particularly, it relates to such element suitably used for a video tape recorder, a video camera and so on.
2. Description of the Prior Art
There has been known an ultrasonic-wave delay element as shown in FIG. 4. In the side view of FIG. 4, a part of a delay medium body 1 made of a material such as glass and having the major surface defined by a rectangular shape is cut at an angle of about 45.degree., and an input electric-mechanic transducer 2 and an output electric-mechanic transducer 3 (herein below referred to as simply to a transducer) are provided in the side A formed by cutting the part of the delay medium body 1. In the ultrasonic-wave delay element of this type, for the purpose of miniaturization of the element, it is usual to design a sound-wave path in such a manner that a single reflection point (a) exists in the cut side A so that the direction of incident of the sound-wave is substantially equal to the direction of reflection of it.
There has also been known an ultrasonic-wave delay element in which a pentagonal delay medium body 1 formed by cutting at an angle of about 45.degree. a part of the major surface defined by a rectangular shape is used, and an ultrasonic-wave propagation path 8' is always in parallel with and perpendicular to the reflected ultrasonic-wave propagation path 8" as shown in FIG. 5 (Japanese Examined Utility Model Publication No. 117/1978).
In the ultrasonic-wave delay element of this type as shown in FIG. 4, the size of the delay medium body 1 can be miniaturized by providing a single reflection point (a) for a sound-wave in the cut side A. It is, however, insufficient for the purpose of miniaturization because of recent demand of reduction in weight and size of a video tape recorder and a video camera, and there is demand of further miniaturization for the ultrasonic-wave delay element.
In the ultrasonic-wave delay element as shown in FIG. 5, there is limitation in miniaturization because it is necessary to determine an ultrasonic-wave propagation path in parallel and vertical to the reflected propagation path.
Generally, the conventional ultrasonic-wave delay element is provided with lead wires which are attached to electrodes (not shown in the drawing) provided on the input and output transducers by, for instance, soldering so that a voltage is applied to the input transducer and a voltage is taken out from the output transducer. However, since the input and output transducers emit sound-waves at the opposite side of the delay medium body to carry out electric-mechanical transducing or mechanical-electrical transducing (herein below referred to as simply electric-mechanical transducing), there takes place irregular reflection of the sound-waves at the lead-wire fitting parts 4, 5 in FIGS. 4 and 5. When the sound-waves regularly reflected are input in the delay medium body through the input and output transducers, the sound-waves being propagated to the output transducer after they have been reflected on a side surface of the delay medium body, the sound-waves are detected as spurious signals (which are indicated by the reference numerals 6 and 7 in FIGS. 4 and 5).
Particularly, when the size of the delay medium body is miniaturized as the above-mentioned ultrasonic-wave delay element, the size of the input and output transducers should also be small, whereby an angle of expansion of the sound-wave becomes large and the positions of the input and output transducers come close with the result that influence by the spurious signals becomes large. For instance, when the ultrasonic-wave delay element having the above-mentioned construction is used for a comb filter circuit or a noise canceller of the video tape recorder, noises in a vertical strip form occur in a reproduced image due to the spurious signals.
If the size of the delay medium body is enlarged, the magnitude of the sprious signals becomes small. On the contrary, however, the size of the ultrasonic-wave delay element becomes as a whole large. This is contradictory to the recent demand of reduction in weight and size.